Overhead conveyors of the rotary drive shaft type are disclosed in U.S. Pat. No. 5,806,655 issued Sep. 15, 1998 to Tabler, in U.S. Pat. No. 5,785,168 issued Jul. 28, 1998 to Beall, Jr., in U.S. Pat. No. 4,203,511 issued May 20, 1980 to Uhing, in U.S. Pat. No. 3,164,104 issued Jan. 5, 1965 to Hunt, and in U.S. Pat. No. 3,850,280 issued Nov. 26, 1974 to Ohrnell. In this rotary drive shaft type of overhead conveyer, one or a plurality of aligned rotary shafts extend along the conveying path, and skewed rollers contact the shafts to be driven linearly along the path as the shafts rotate, with the rollers being attached to the carriage for free relative rotation.
One environment wherein the overhead conveyor is used is that employing a high temperature, for example within an oven. Conveyers of the rotary drive shaft type are often used to feed to, pass through and exit from ovens, for example as set forth in U.S. Pat. No. 5,919,023 issued Jul. 6, 1999 to Owens, whose disclosure is incorporated herein in its entirety, by reference.
An alternative to the drive shaft overhead conveyer is a power and free chain driven conveyor. Overhead chain conveyers are well known, and they generally have an endless chain (a chain attached to itself in a loop and passing around two or more sprockets, one of which is driven) that carries a plurality of loads or pushers for loads.